An internal combustion engine derives power from the volumetric compression of a fuel-air mixture, followed by a timed ignition of the compressed fuel-air mixture. The volumetric change generally results from the motion of axially-reciprocating pistons disposed in corresponding cylinders. In the course of each stroke, a piston will vary the gas volume captured in a cylinder from a minimum volume to a maximum volume. In an Otto cycle, or “four-stroke” internal combustion engine, the reciprocal motion of each piston compresses the fuel-air mixture, receives and transmits the force generated by the expanding gases, generates a positive pressure to move the spent gases out the exhaust port and generates a negative pressure on the intake port to draw in a subsequent fuel-air gas charge.
The modern internal combustion engine arose from humble beginnings. As early as the late 17th century, a Dutch physicist by the name of Christian Huygens designed an internal combustion engine fueled with gunpowder. It is believed that Huygens' engine was never successfully built. Later, in the early nineteenth century, Francois Isaac de Rivaz of Switzerland invented a hydrogen-powered internal combustion engine. It is reported that this engine was built, but was not commercially successful.
Although there was a certain degree of early work on the idea of the internal combustion engine, development truly began in earnest in the mid-nineteenth century. Jean Joseph Etienne Lenoir developed and patented a number of electric spark-ignition internal combustion engines, running on various fuels. The Lenoir engine did not meet performance or reliability expectations and fell from popularity. It is reported that the Lenoir engine suffered from a troublesome electrical ignition system and a reputation for a high consumption of fuel. Approximately 100 cubic feet of coal gas were consumed per horsepower hour. Despite these early setbacks, a number of other inventors, including Alphonse Beau de Rochas, Siegfried Marcus and George Brayton, continued to make substantial contributions to the development of the internal combustion engine.
An inventor by the name of Nikolaus August Otto improved on Lenoir's and de Rochas' designs to develop a more efficient engine. Well aware of the substantial shortcomings of the Lenoir engine, Otto felt that the Lenoir engine could be improved. To this end, Otto worked to improve upon the Lenoir engine in various ways. In 1861, Otto patented a two-stroke engine that ran on gasoline. Otto's two-stroke engine won a gold medal at the 1867 World's Fair in Paris. Although Otto's two-stroke engine was novel, its performance was not competitive with the steam engines of the time. A successful two-stroke engine would not be developed until 1876.
In or around 1876, at approximately the same time that an inventor named Dougald was building a successful two-stroke engine, Klaus Otto built what is believed to be the first four-stroke piston cycle internal combustion engine. Otto's four-stroke engine was the first practical power-generating alternative to the steam engines of the time. Otto's revolutionary four-stroke engine can be considered the grandfather of the millions of mass-produced internal combustion engines that have since been built. Otto's contribution to the development of the internal combustion engine is such that the process of combusting the fuel and air mixture in a modern automobile is known as the “Otto cycle” in his honor. Otto received U.S. Pat. No. 365,701 for his engine.
Ten years after Klaus Otto built his first four-stroke engine, Gottlieb Daimler invented what is often recognized as the prototype of the modern gasoline engine. Daimler's engine employed a single vertical cylinder, with gasoline imparted to the incoming air by means of a carburetor. In 1889, Daimler completed an improved four-stroke engine with mushroom-shaped valves and two cylinders. Wilhelm Maybach built the first four-cylinder, four-stroke engine in 1890. The carbureted four-stroke multi-cylinder internal combustion engine became the mainstay of ground transportation from the early 1900s through the 1970s, ultimately being supplanted by fuel-injected engines in the 1980s.